There are three different types of fighting styles that are in the game, to use one, you must first get your muscle strength up to "buff" by working out in the gym. Next go fight the master of the gym that you are in by stepping into the red marker next to him. Once you defeat the master of the gym, he will show you different attacks that you now have, you use these with the triangle button. If you beat the master of the Los Santos gym, you now learn some boxing moves, the San Fierro gym, Martial Arts, and the Las Venturas Gym, Kick Boxing. The moves you currently have depend on the last master that you defeated.